Space pic of the week: Curiosity’s view of the Martian dust storm

Curiosity captured this sequence of the apocalyptic-looking dust storm that swept across Mars.

Curiosity Rover used its Mast Camera, or Mastcam, to snap photos of the intensifying haziness the surface of Mars, caused by a massive dust storm. The rover is standing inside Gale Crater looking out to the crater rim. The photos span about a couple of weeks, starting with a shot of the area before the storm appeared. Credit: NASA

A storm of tiny dust particles engulfed much of Mars this month, causing NASA’s Opportunity rover to suspend science operations. But on the other side of the planet the Curiosity rover remained largely unaffected by the dust.

While Opportunity needed to power down as its solar panels were unable to collect sunlight, the nuclear-powered Curiosity continued operation, including snapping these images of the dust storm as it occurred.

As the dust storm encircled the planet, it blocked the sunlight at levels never before seen. At Curiosity’s location at Gale Crater the atmospheric haze blocking sunlight, called “tau,” topped 8.0, six to eight times thicker than normal, while at Opportunity’s site it was over 11.0.

The sequence above depicts Curiosity’s view of the Gale Crater rim about 30 kilometres away. The photos, taken by its Mast Camera show the sky getting hazier as the storm rolls in.

While Opportunity needed to power down to ride out the storm, there was actual little risk to the rovers themselves. In fact, according to engineers at JPL, the biggest impact the storm has is that the cameras require extra exposure time due to the low lighting.

As Mars’ atmosphere is so thin – around 1% of Earth – there is also little risk of the rovers being blown over, or being sandblasted by the dust itself. Winds on Mars reach their peak at around 100 kilometres an hour, but the thin atmosphere means the effect of those winds is less than what would be the case on Earth.

The bigger issue is the dust settling and sticking to the equipment. Dust can grit up the mechanicals of the rovers, and coat Opportunity’s solar panels. To prevent dust build up on the lens of Mastcam, Curiosity already routinely points it at the ground after each use.

Change in light

Two images from the Mast Camera (Mastcam) on NASA’s Curiosity rover depicting the change in the color of light illuminating the Martian surface. The cherry red color is due to red dust grains in the atmosphere letting red light through to the surface, but not green or blue, and to different exposure times for the two images. Credit: NASA/JPL-Caltech/MSSS

These images also taken by Curiosity show the change in the colour of light inside the Gale Crater caused by the dust storm.

The difference in colour is due to two main reasons, NASA say. Firstly, with darker conditions the exposure time of the camera is nine-times longer, increasing from a normal exposure of 7.3 milliseconds to 66 milliseconds.

However the main cause of the change is the filtering of red light by the dust. Very little green and essentially no blue light makes it through the dust cloud, creating a deep red hue at ground level.

Also of note is the extra detail on the shadowed side of the rock. With the sky filled with dust and reddened, the rock is effectively illuminated from all sides.

A selfie by Curiosity as the dust storm approached. Credit: NASA/JPL-Caltech/MSSS

Martian dust storms

Dust storms on Mars are quite common, however they usually stay confined to the local area. This global dust storm, however, afforded NASA scientists an unprecedented opportunity to study the Martian phenomenon, and investigate why some storms grow so big they encircle the planet while others stay small and localised.

Between Curiosity and orbiting spacecraft, there was a multitude more equipment available to measure the event than ever before. The last storm of global magnitude that enveloped Mars was in 2007, five years before Curiosity landed there.

Dust storms form during the southern hemisphere’s summer when the planet is closest to the Sun. Winds pick up, generated by contrasts in surface temperatures between areas. These winds pick up dust grains the fineness of talcum powder.

In addition, carbon dioxide on the polar ice caps evaporates, thickening the atmosphere and helping suspend the dust particles in the air.

About the Author

Ben Lewis
Ben Lewis is the Editor of Australia’s Science Channel, and a contributor to Cosmos Magazine. He has worked with scientists and science storytellers including Brian Cox, Chris Hadfield, Robert Llewellyn, astronauts, elite athletes, Antarctic explorers, chefs and comedians. Ben has also been involved in public events around Australia and was co-writer, producer and director of The Science of Doctor Who, which toured nationally in 2014 in association with BBC Worldwide Australia & New Zealand. Want more Ben? You can hear him on ABC and commercial radio in Adelaide, regional SA, across NSW, and the ACT. He also speaks at universities around Australia on communicating science to the public. Around the office he makes the worst jokes known to mankind.

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